This invention relates to motor control centers having compartmentalized cabinets for receiving removable control units which are inserted or withdrawn through open fronts of the respective compartments. More particularly, this invention relates to an operator mechanism which is accessible to the exterior of the cabinet for operating circuit interrupting apparatus mounted on a respective removable control unit disposed within the cabinet.
Motor control centers comprise a cabinet having a plurality of vertically arranged compartments which open to a forward face of the cabinet. The individual compartments may be of varying height, and each comprise a door individual to the respective compartment for closing off the same. Removable motor control units are insertably received individually within the respective compartments from the open front thereof, such units having motor control apparatus comprising circuit interrupting apparatus such as circuit breakers or fusible disconnect switches mounted therein. Such circuit interrupting apparatus has its own operator mechanism, but auxiliary operating mechanisms are provided on the control unit which enable the apparatus to be operated from the exterior of the motor control center cabinet. These auxiliary operator mechanisms are commonly mounted at the forward edge of the control unit and are accessible exteriorly of the cabinet through openings provided in the respective door of the cabinet. A requirement of motor control center design is that the uppermost position of the handle for the auxiliary operator mechanism for the uppermost compartment be no more than a certain maximum height as measured from the floor to permit operation thereof by a workman of average height without need for a ladder, step or hook device. Accordingly, this requirement places certain restrictions on the design and operation of the auxiliary operator mechanism with respect to handle throw.
Another factor to be considered in the design of auxiliary operator mechanisms is non-interference of the operator handle with the opening in the door when the door is swung to its open position. The width of the opening is determined by the forwardmost position of the operator handle with respect to the arc defined by the door. The vertical dimensions of the opening are determined by the uppermost and lowermost positions of the operator handle. Since the auxiliary operator mechanism is mounted on the front of the control unit, it is desirable that the frontal dimensions be as small as possible to minimize any access restriction to the panel space of the control unit behind the mechanism. However, it is necessary that the housing of the auxiliary operating mechanism be wide enough to fill the opening in the door to provide proper sealing for the control center.
Another concern in providing an auxiliary operator mechanism for motor control centers is a requirement that the operator mechanism have provisions for locking the operator handle in the OFF or ON position. The operator mechanism should be capable of locking the handle in the OFF position with as many as three padlocks whereby maintenance personnel may operate the respective motor control unit to its OFF condition and lock the handle in that position with a personal padlock or similar locking device to enable work to be performed on equipment controlled by that unit with the assurance that power cannot inadvertently be restored by another individual operating the mechanism to an ON condition. It is occasionally desirable to enable the handle to be locked in the ON position, although this locking feature commonly requires the maintenance worker to make some conscious modification of the operator mechanism in order to accomplish locking in the ON position.